In a recent blog post Adobe announced pricing for Creative Cloud, which, among other things will offer subscription pricing for Creative Suite products.
But also in this blog post is the folowing nugget:
"With regards to upgrades, we are changing our policy for perpetual license customers. In order to qualify for upgrade pricing when CS6 releases, customers will need to be on the latest version of our software (either CS5 or CS5.5 editions). If our customers are not yet on those versions, we’re offering a 20% discount through December 31, 2011 which will qualify them for upgrade pricing when we release CS6."
So, if you don't think you'll be enrolling in Creative Cloud, but prefer a perpetual license, it might be smart to upgrade to CS5.5 while you can.